Process of preparing a precious-metal-dissolving means.



TTED STATES PATENT OFFICE.

HANS FOERSTERLING, OF PERTH AMBOY, NEW JERSEY, ASSIGNOR TO THE ROESSLER& HASSLAGHER CHEMICAL (30., OF NEW YORK, N. Y., A CORPORATION OF NEWYORK.

PROCESS OF PREPARING A PRECIOUS-METAL-DISSOLVING MEANS.

Specification of Letters Patent.

Patented Oct. 14, 1913.

No Drawing. Original application filed September 21, 1909, Serial No.518,735. Divided and this application filed December 7, 1810.

To all whom it may concern:

Be it known that 1, Thus Founs'rnnmuo, a subject of the Emperor ofGermany, residing at Perth Amboy, county of Middlesex, State of NewJersey, have invented a new and useful Process of Preparing aPrecious-Metal-Dissolving Means, of which the following is aspecification.

My invention relates to a process of preparin a precious metaldissolving means which will easily generate halogen cyanids inconnection with an oxidizing agent, and is a division of my applicationSerial No. 518,735, filed September 21, 1909.

it has been found advantageous, in practising the well known cyanidprocess in the treatment of certain ores, to add some means ofoxidation, as for instance air, barium peroxid, per-sulfates, ozone,etc. It has further been found that halogen cyanids give a very good andquick extraction of the precious metals from complex ores liketellurids. The so-called Diehl process, which makes use of bromo cyanid,is extensively practised in Australia with good results, but as bromocyanid is extremely poisonous and very volatile it has heretofore beenprepared only just before it is used and can be produced only by theexer cise of the greatest skill and care.

The usual practice heretofore, in making bromo cyanid, has been to mixsulfuric acid in a tank with water and allow the solution to cool.Cyanid is then dissolved in an other tank and the cyanid solution addedto the cooled diluted sulfuric acid. At the same time a mixture of analkali bromid and bromate is added under stirring. The reaction takesplace according to the following equation:

It is obvious that the manufacture of bromo cyanid as heretoforepractised for this purpose is not simple and that great care must betaken in order to obtain good results. If the mixture of the alkalibromid and bromate is not the correct one, bromin is wasted.

In the following I have described one means of practising my new methodof preparing my new precious metal dissolving Serial No. 596,138.

means: I melt an alkali halogen, for instance sodium bromid with analkali cyanid, for instance sodium cyanid, in the proportion of onemoleculeof sodium bromid to one molecule of sodium cyanid and permit thesame to solidify. I have discovered that no decomposition takes placeduring this process. This double salt of sodium bromid and sodium cyanidis used instead of the mixture heretofore used consisting of sulfuricacid, sodium bromid', sodium bromate and cyanid. In order to convertthis double salt of sodium bromid and sodium cyanid into bromo cyanid Iadd an oxidizing agent, for instance an acid solution of hydrogenperoxid, the reaction taking place according to the following equation:

If an acid solution was not used sodium hydrate would be formed whichwould destroy the bromo cyanid according to the following equation:

The rapidity of the formation of bromo cyanid according to the aboveformula depends somewhat on the concentration of the solution. I havefound that if T pour a 25 7 volume hydrogen peroxid solution, to whichthe required amount of sulfuric acid has been added, over the doublesalt of sodium cyanid and sodium bromid the formation of bromo cyanid issorapid that I have to cool the mixture. Bromin is seen to evolve and isat once taken up by the hydro cyanic acid. The bromo cyanid is boiling,but it can be easily condensed by proper cooling. If I dissolve 15 gramsof sodium cyanid plus sodium bromid in 150 com. water and add to thissolution 150 com. of water containing 8.4 grams hydrogen peroxid and 10grams sulfuric acid the reaction takes place without necessitatingcooling. If I use the same amounts of sodium cyanid plus sodium bromidand hydrogen peroxid plus sulfuric acid in 2000 ccm. of water apparentlyno reaction takes place, but by leaving the solution standing the bromocyanid can be easily detected after a while by its characteristic.

smell. I have found that the formation of chlorin cyanid and iodincyanid, according to the same formula, is more rapid than the formationof bromo cyanid.

instead of using an acid solution of hydrogen peroxid, an alkali peroxidcan be dissolved in an excess of an acid, or any other oxidizing agentcan be used which will convert the eyanid double salt into halogencyanid.

By the practice of my invention the mines receive the ready madecorrectly proportioned mixture of alkali halogen with the eyanid, allthat is necessary being to dissolve a certain amount of the double saltand add an oxidizing agent.

In order to dissolve gold by the use of bromo cyanid, 3 parts of alkalicyanid should be added to 1 part of bromo cyanid, according to thefollowing equation:

I can add sutticient cyanid at the beginning to the alkali halogen sothat I obtain a mixture equivalent to the sum of the two equations:

Furthermore, the largest part of the alkali halogen is not lost inpractical mill Work, and I therefore have to add only so much alkalihalogen to the cyanid as is actually lost.

As an oxidizing agent I prefer to use an acid hydrogen peroxid solution,as it can be easily made by dissolving sodium peroxid in an excess of anacid. Such acid solutions of hydrogen peroxid, as is Well known, arevery stable.

It must be understood that I do not limit myself to the use of a mixtureof sodium bromid and sodium cyan'id and the use of hydrogen peroxid asan oxidizing agent. Instead of an alkali bromid another alkali halogencan be used which is able to form a halogen cyanid, as for instancealkali iodid. Instead of a mixture of an alkali halogen and alkalicyanid melted together and solidified I can use a double salt obtainedby evaporating a solution of an alkali halogen and an alkali cyanid;instead of using an acid solution of hydrogen peroxid I can use anyother oxidizing agent; instead of using sodium as the alkali I can useany other suitable alkali such as potassium.

lVhat I claim and desire to secure by Letters Patent is:

1. A process of preparing a precious metal dissolving means consistingin forming a homogeneous solidified mixture oi? an alkali cyanid and analki li halogen and dissolving the same in the presence of an oxidizingagent.

2. A process of preparing a precious metal dissolving means consistingin fornr ing a homogeneous solidified mixture of sodium cyanid andsodium bromid and dissolving the same in the presence of an oxidizingagent.

3. A process of preparing a precious metal dissolving means consistingin torming a homogeneous solidified mixture of an alkali cyanid and analkali halogen and dissolving the same in the presence of an acidsolution of a suitable peroxid.

at. A process of preparing a precious metal dissolving means consistingin forming a homogeneous solidified mixture of sodium cyanid and sodiumbroinid and dissolving the same in the presence of an acid solution of asuitable peroxid.

5. A process of preparing a precious metal dissolving means consistingin forming a homogeneous solidified mixture of sodium cyanid and sodiumbromid and dissolving the same in the presence of an acid solution ofhydrogen peroxid.

In testimony whereof I have signed this specification in the presence oftwo subscribing Witnesses.

HANS FOER S E lLl NG.

lVitnesse-s D. Grouse, J11,

Aux om) Nnuxnx nnno.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents, Washington, D. G.

